For improved thermodynamic efficiency of a gas turbine engine, a high pressure turbine section of the engine may be operated at its highest possible temperature. However, the operating temperature of the turbine increases, so do thermal stresses on turbine airfoil components, such as blades and vanes. These stresses may result in reduced lifetime of the components and potential failure during operation. Modern aircraft turbine engines, as well as ground-based turbines for power generation, have addressed the seemingly divergent requirements for higher operating temperatures and protection and preservation of the turbine airfoils with significant advances in design, materials and manufacturing technologies.
Modern turbines airfoils are generally constructed of metallic superalloys, which provide superior mechanical strength, resistance to creep, oxidation and corrosion, and long fatigue lifetimes at high temperatures compared to conventional metals and alloys. High temperature performance can be further enhanced by a network of internal cooling channels that allow circulation of a cooling fluid (typically air) through the airfoil. Exhaust ducts and holes in the airfoil surface expel air from the internal channels. The holes may be designed to direct a film of cooling fluid along the exterior surface of the airfoil to further enhance cooling.
Various method of using infrared thermography can be used to detect blockages in holes of a component, such as cooling holes of an airfoil. Generally, the methods typically involve pumping a fluid (either hot, cold or alternating hot and cold) through the component and then viewing the resulting infrared image of a surface of the component to determine if the fluid is properly expelled from all holes of the component. In some cases, the gas is chosen to be visible in the infrared spectrum. In other methods, the input and exhaust pressures of the gas are closely monitored with sensors, and deviations in the relationship between these pressures is taken to be an indication of blockage. These methods are generally successful in detecting complete, or near complete blockages, but they are often unable to detect partial blockages.